Using flash in ble_app_uart application on nRF52833

Hi,
I'm developing an application include features

ble, 2 libuartes, pwm, timer and now I'm planning add flash to my application

1. I'm using flash_fds. I find cli.c using uart, but I'm don't know clearly about this cli. what is cli used for ?
2. Is there any simple way to use flash, I just write and read from them basically.? 
3. Can you explain flash's code example for me to approach esier ?

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